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When you're out in the field spraying herbicides, you're not just applying a chemical — you're creating a complex mixture. A crucial, and often overlooked, component of that mixture is the water you're using.
The quality of your water can dramatically affect how well an herbicide works, or if it works at all. Water quality plays a significant role in spray efficacy, primarily your water:
pH
Hardness
Turbidity
Temperature
Water pH is a measure of its acidity or alkalinity. The scale runs from 0 to 14, with 7 being neutral.
The ideal pH for many herbicides is slightly acidic, typically between 4.0 and 6.0.
In this range, the herbicide molecules remain in their undissociated form, making it easier for them to penetrate the waxy leaf cuticle of a weed. In contrast, highly alkaline water (pH above 7.0) can cause the herbicide molecules to dissociate. This process, known as alkaline hydrolysis, creates negatively charged molecules that struggle to enter plant cells. This can significantly reduce the herbicide's effectiveness.
While many herbicides, particularly weak-acid herbicides like glyphosate, 2,4-D, and dicamba, perform best in slightly acidic water (pH 4-6.5), some specific products, such as sulfonylurea herbicides, actually prefer a slightly alkaline environment.
Always check the herbicide label before spraying. The product label is the primary source of information and will often specify the recommended pH range for the spray solution. Some newer products are formulated with built-in buffers, while others are highly sensitive to pH. Understanding the recommended range is the first step to knowing if you need to adjust your water at all.
To adjust your water pH to the optimal range for the specific product you're using:
1. Add an Acidifier or Buffering Agent: These products are specifically designed to lower and stabilize the pH of the water. Examples include ammonium sulfate (AMS), commercial pH buffers, and citric acid or phosphoric acid.
2. Conduct a Jar Test: This test allows you to determine the exact amount of additive needed per gallon or liter of water to achieve the target pH. It prevents you from over- or under-acidifying the solution, which can also be harmful to some herbicides.
3. Adjust the Mixing Order: Always add the water conditioner or buffering agent to the water first, before adding any herbicides or other products. This ensures the water is at the correct pH before the herbicides are introduced, preventing them from degrading immediately. A typical mixing order would be:
Water
Water conditioner/buffer
Wettable powders or dry flowables
Suspension concentrates
Emulsifiable concentrates
Surfactants and other adjuvants
Herbicides (e.g., glyphosate, 2,4-D)
Water hardness is a measure of dissolved mineral salts, primarily calcium (Ca2+) and magnesium (Mg2+).
These positively charged ions can bind with negatively charged herbicide molecules in the spray tank, forming inactive, insoluble salts. This is especially true for herbicides like glyphosate. The hard water ions essentially "tie up" the active ingredient, preventing it from being absorbed by the plant.
To address excess water hardness, many herbicide labels recommend adding a water conditioner like ammonium sulfate (AMS). AMS works by preferentially binding with the hard water ions, leaving the herbicide molecules free to do their job.
Turbidity refers to the cloudiness or haziness of the water, which is caused by suspended particles like clay, silt, and organic matter. These particles can have a high surface area and tie up herbicide active ingredients.
For example, glyphosate can be strongly adsorbed onto clay particles. If your water source is from a pond or ditch with high turbidity, a significant portion of your expensive herbicide may bind to these particles and never reach the target weed.
When your water is too turbid or muddy before spraying, try the following steps to improve water quality:
1. Let the Water Settle: If possible, the simplest solution is to let the water sit in the tank overnight. The heavier clay and silt particles will settle to the bottom, leaving clearer water on top. You can then carefully pump the cleaner water from the top of the tank, avoiding the settled sediment at the bottom.
2. Use a Water Conditioner: The most common and effective solution is to add a water conditioner to the spray tank. Products like ammonium sulfate (AMS) are highly recommended for this purpose. The ammonium in AMS helps to neutralize the negative charges on the clay particles, causing them to clump together and settle out of the solution more quickly. This also frees up the herbicide molecules that may have been tied up by the clay.
3. Adjust the Mixing Order: When using a water conditioner to combat turbidity, the mixing order is crucial. You should add the water conditioner to the water first and allow it to mix thoroughly for several minutes. This gives the conditioner time to work on the clay particles before the herbicide is added. A proper mixing order would be:
Fill the tank with water.
Add the water conditioner (e.g., AMS) and circulate.
Add the herbicide and other products as recommended by the label.
4. Consider a Dedicated Surfactant or Adjuvant: Some specialty adjuvants are specifically designed to help with water quality issues, including high turbidity. These products can help keep the herbicide in solution and prevent it from binding to the clay particles. Always check the herbicide label for recommendations on specific adjuvants.
Water temperature can also influence efficacy, though it is somewhat less influential than water pH or water hardness.
Using extremely cold water can slow down the dissolution of dry herbicides and some adjuvants. It can also reduce the overall chemical reaction rate in the tank, potentially affecting tank-mix compatibility.
The first step in addressing water quality issues is to test your water. Simple kits and meters are available to measure pH and hardness. Once you know your water's characteristics, you can make informed decisions.
Ignoring water quality is like building a house on a weak foundation. By paying close attention to your water, you can ensure that your herbicide applications are as effective as possible, leading to better weed control and a healthier bottom line.
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